Experimental Characterizations of an Aging Mechanism of Sands

Abstract

Sands age and their engineering properties often improve significantly during performance life cycles and are of practical interest to engineers. Although various hypothesized aging mechanisms have been proposed, experimental evidences identifying the underlying mechanisms have not yet been provided. The experiment of this study, using a true triaxial apparatus equipped with the bender element and tactile pressure sensor, is therefore designed to complement this missing part. The experimental results show a distinct and continuous increase in the measured small-strain shear modulus of a dry, predominately quartz sand sample, subjected to a constant confining pressure for 30 days of aging, during which the measured volumetric strain is negligible. In addition, the measured contact normal forces (by the tactile pressure sensor) continuously redistribute and ultimately become uniform over time, i.e., the process of contact force homogenization. Sand particles in the weak force network gradually share the forces that are redistributed from the strong force network. These findings indicate that the weak contact force network in sand is gradually strengthened, thus reinforcing the soil structure and giving rise to a higher small-strain shear modulus during aging.